Microtitration trays and frangibly-connected multi-well strips for use in such trays are well-known. See, for example, Lyman et al. U.S. Pat. No. 5,110,556 for "Multi-Well Test Plate", and Verwohlt et al. U.S. Pat. No. 5,514,343 for "Microtitration System." The tray in Lyman et al. is an open tray with no apertures for the wells. The tray of Verwohlt et al. has elongated double well apertures with opposing retention members. Other configurations such as in Thorn et al. U.S. Pat. No. Re 34,133 include trays in which the compartments are defined by rows and columns of posts upstanding from the tray.
In a common modern form of a microtitration tray, the tray is formed with a plurality of circular apertures in a top panel in which are placed arrays of wells, frangibly-connected into a series of strips so that each strip contains a linear array of a plurality of wells. The wells can be cylindrical but often frustoconical in shape wherein a lower portion of the well is smaller in diameter than the aperture in the tray while the diameter of an upper portion is progressively larger until it binds with the tray for a friction fit. An advantage of such a combination of circular apertures and frustoconical wells is the ability of the tray to securely constrain the wells against movement during various operations. If the well is cylindrical, then it will be somewhat loose in the tray aperture or will require a very fine manufacturing tolerance to be close fit to the aperture.
These problems are solved with a frustoconical well. However, while solving one problem, another problem is introduced and that is the inability of such wells to be readily released from the tray. This is particularly troublesome with wells that are frangibly connected to form a linear, multi-well strip. Such strips typically contain eight wells and when it is desired to remove the strip, the strong frictional engagement of each of the eight wells results in a cumulative retention effect making it very difficult to easily remove the strip without the danger of breaking the frangible connection of one or more wells.